$A$ stretched string of length $l,$ fixed at both ends,can sustain stationary waves of wavelength $\lambda,$ given by:

• A
  $\lambda = \frac{n^2}{2l}$
• B
  $\lambda = \frac{l^2}{2n}$
• C
  $\lambda = \frac{2l}{n}$
• D
  $\lambda = 2ln$